Copy errors passim (eg, [g] for [y]) confirm the 1756 colophon in attributing this ms to learnèd polymath admiral Roland-Michel Barrin, comte de La Galissonière. French postvocalic-s spellings might date the missionary original to as early as the 1660s, but Barrin could have copied it at any time after his first visit in 1711, altho most likely in 1747-9, during his acting governorship, when he promoted Picquet at the Oswegatchie mission.
Errata here: de l'Agnie -> d'Agnié (&c)